The essence of nervous system organization is the establishment of synaptic circuits. A great deal of precision is demanded in the construction of these circuits, and many of the disorders of behaviour that occur in humans and other animals are due to abnormalities in the development of synaptic connections. The long-term objectives of this research are to elucidate basic cellular and molecular mechanisms which underlie the formation and maintenance of specific synaptic connections, using the terminal ganglion of the cockroach as a model system. Many of the mechanisms which control other aspects of neuronal development have been shown to be conserved throughout evolution, which makes it likely that this work will contribute to our eventual understanding of how our own brains are assembled. The first specific aim of this project is to determine the sequence and specificity of synapse formation between identified neurons during embryonic development, using intracellular recording, dye injection and light and electron microscopy. The second aim is to assess the accuracy with which cercal afferents regenerate their arborization and synaptic connections, using a combination of intracellular recording, dye injection, and morphometric analysis. The third specific aim is to determine the physiological and anatomical basis for synaptic competition in mutant cockroaches with a supernumerary presynaptic neuron, using a combination of quantal analysis and quantitative electron microscopy. Intracellular dye injection will be used to find out whether the supernumerary axon arrives later in the terminal ganglion than the normal axons. The effect of synchronized regeneration on the relative synaptic efficacies will be investigated. Intracellular recording and dye injection will be used to pursue the fourth aim of this project; to determine the role of competitive interactions during postembryonic development of genetically wild-type animals.